Switching devices of this type with corresponding, generally electromagnetic drives are for example used in motor starters. These are to be suitable for the functional switching of a load, switching off an overload and switching off in the event of a short circuit. Basically, to achieve this functionality, two separate switching devices can also be used, namely a motor protection switch as the power switch and a contactor as the load switch. Alternatively, motor starters are known, in which the switching and protection function is integrated in one switching device. Generally, these have for this purpose a hand-operated, mechanical switching lock.
In document WO 2014/023326 A1, a switching device or a drive for a switching device for a compact and remotely-operated motor starter is described, with which the functional switching of the load, switching off the overload and switching off short circuits is to be implemented with only one device. The problem in switching off short circuits is the necessity to break the contacts made very quickly and permanently, so that a safe extinguishing of the arc is ensured and a re-ignition of the arc and a welding of the contacts are avoided. For this purpose, the drive has a bipolar electromagnetic drive unit having a movable armature and two stationary magnetic coils for the reversible movement of the armature between two permanent-magnetically stabilized armature positions, wherein a movable contact can be moved into the contact-making position by selective excitation of the first magnetic coil, and the movable contact can be moved within a maximum switching-off time, which is permissible for a short circuit in the current path, into the contact-breaking position by selective excitation of the second magnetic coil.
Electromagnetic drives, which are used for on-off switching, have the drawback that they have a comparatively large, moving mass, which is necessary for the switching-on process. Because of inertia, a drive of this type has a correspondingly long switching-off time, however. The switching-off times that can thus be achieved can potentially be too long to safely switch off a short circuit.